Over six days of driving—limited to around-town trips—we put about 103 miles on a fleet-test Toyota Prius Plug-In, averaging 90.8 miles per gallon. In that time, we gave the Prius Plug-In five full charges and two partial ones, and according to the trip computer, we covered 77.7 miles in EV mode.
As we've reported in prior driving impressions, the Plug-In, which won't go on sale until spring of 2012, will move on—or primarily on—electric power for up to 14 or so miles per charge, and a full charge only takes about three hours with a standard 110V household power outlet.
There are several conversation points here, and it takes some juggling of figures to get a grasp of whether the plug-in might be right for you. That starts with two big questions: Firstly, how much does the Prius cost to run on electric power versus normal hybrid operation; and secondly, what's the net difference in carbon footprint and emissions?
Both of those answers are going to be dramatically different from family to family, depending on how often you remember to plug in, how far you travel per trip and each day, and whether it's possible or convenient at waypoints.
Charges cost less than 50 cents a pop
First, the cost-of-ownership question. According to Toyota spokesman John Hanson, the Prius PHEV only uses about 3.8 kWh of the battery's 5.2-kWh capacity (for battery longevity). Starting with what electricity costs me here in Portland, Oregon—11.7 cents per kWh, slightly higher than the 11.04-cent national average at the end of last year—that pegs each full charge at about 44 cents. With a total of about six charges, given the five full charges and two partial ones, that puts our total cost of electricity at about $2.67.
In a driving style that's comparable to what we followed with the Plug-In—which is to say gentle and careful, with only a couple of exceptions to test the power on tap—we've seen in the range of 48 mpg in the standard Toyota Prius. So we would have used about 2.15 gallons of gasoline in a non-Plug-In model. At the current national average of about $3.54 a gallon, that's $7.61 in a standard Prius to cover those 103 miles. In our PHEV test car, we used 1.13 gallons ($4.01), plus that $2.67 in electricity—bringing our total for the PHEV of $6.68.
Just to index this in some way, here it is adjusted for 100 miles, at the average cost of residential electricity:
Prius Plug-In (100 miles): $6.12
Standard Prius (estimate, 100 mi): $6.98
Difference per 100 miles: $0.86
Difference per 10,000 miles: $86
Difference per 100,000 miles: $860
Payback? Probably not.
With the 2012 Toyota Prius Plug-In expected to sell at $3,500 to $5,000 more than a comparable Prius, payback in this traditional sense probably isn't going to happen—even if gas prices double.